Character of lubrication is critical for extending spindle speeds to progressively higher and higher r.p.m. without overheating and the consequent bearing failure, thereby accomodating progressively increased cutting speeds for machining operations made possible by technological improvements in cutting tools. Such increased spindle speeds are particularly important in high volume machining operations for automotive production parts and the like, where any reduction in cycle time through increased machining speeds can result in corresponding savings in manufacturing costs.
Typical spindle bearings involve two pairs of axially spaced ball or tapered roller thrust bearings where effective lubrication is essential. Conventional lubrication may involve packing the bearings with grease serviced periodically as through Alemite fittings. R.P.M. limitations arise when the grease overheats, oxidizes, and loses its lubricating properties.
Gravity fed and injector oil lubrication systems have been employed in order to achieve spindle speeds greater than with grease lubrication. It has been found in such systems that excess oil is a detriment and that minimization of accurately controlled sufficient lubrication offers the greatest potential for maximizing spindle speeds. Injectors capable of small quantity feed in the order of 0.004-0.005 cubic inch per stroke have been employed with air entrainment at the outlet of the injector for delivery through variable length tubing to nozzle outlets at the spindle bearings; such systems do not employ a pressurized oil capillary tube for delivery to the nozzle.
Prior art systems currently in use for spindle bearings include the "Trabon Spindleguard" system and "Bijur Systems" which deliver periodic injection of lubrication through a tube with 0.004-0.005 cubic inches per injection, (0.066-0.082 milliliters) as well as an Alemite system for delivering a continuous mist of lubricant. Maximum spindle speeds up to 600,000 dn (bearing diameter in millimeters times r.p.m.) have been obtained by such lubricating systems believed to be limited by uncertainty of precise control of the quantity and timing of lubrication. Prior art in lubricating cylinder walls in engine assembly plants includes injection through pressurized capillary tubing of 0.080 milliliters per rapid cycle stroke for five seconds with unregulated air pressure in the order of 80 p.s.i. delivered to the nozzle through a tube having approximately 1/10 inch ID for the five second injection cycle.